Research shows people who have precancerous polyps removed have an altered gut microbiome for around 12 years after undergoing surgery, which may explain why there is a significant risk of progressing to colorectal cancer in these individuals despite the surgery.
“Early detection and resection of adenomas through colonoscopy are critical strategies for preventing colorectal cancer. However, individuals with a history of adenoma resection remain at a higher risk of developing colorectal cancer than those without adenomas,” write lead author Mingyang Song, MBBS, ScD, associate professor of clinical epidemiology and nutrition at Harvard University, and colleagues in Cell Host & Microbe.
“Meta-analyses of stool metagenomes from diverse populations have identified consistent microbial biomarkers largely characteristic of later-stage colorectal cancer… Studies investigating the gut microbiome of adenoma patients and along the adenoma-carcinoma continuum have also reported distinct, dynamic microbial shifts from early neoplasia to advanced colorectal cancer.”
This earlier research suggests a link between the gut microbiome and colorectal cancer. It is possible some of these changes arise early in the disease process and act as drivers of the cancer, but what these changes look like remains unclear.
In this study, the researchers analyzed stool samples from 354 women who had colorectal adenomas removed an average of 12 years earlier and compared them to 354 matched controls without polyps. The team used shotgun metagenomic sequencing to analyze fecal metabolites and the composition of the gut microbiome.
The investigators then compared the microbiome data from the women who had adenomas removed and the controls to those from 1,045 people with colorectal cancer enrolled in earlier colorectal cancer studies.
Women who had precancerous polyps removed still showed some gut microbiome changes similar to those seen in colorectal cancer patients. The similarity was modest: only about 7% of the microbiome differences could be attributed to their disease history while 93% came from individual factors like diet, genetics, and lifestyle.
Overall, 31 bacterial species showed consistent changes in both adenoma and cancer cases compared to controls. For example, levels of Faecalibacterium prausnitzii, a bacteria thought to be protective of the gut due to anti-inflammatory properties, were low and levels of potentially harmful bacteria Flavonifractor plautii were enriched.
“The fact that colorectal cancer-associated gut microbial and metabolic features are still detectable a decade later suggests the gut microbiome may be part of sustained colorectal cancer risk,” said first author Ana Nogal, PhD, postdoctoral research fellow at Harvard, in a press statement. “Diet and lifestyle were closely tied to these microbes, raising the possibility that these habits could influence the gut environment in people at higher risk.”
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